Mechanical piston assemblies have a number of applications. In some applications, one or more piston assemblies may be used as a locking mechanism, such as a rotor lock in which the piston serves as an actuated locking pin in an unretracted configuration to lock a rotor in a predetermined orientation. When not in use to lock the system, the piston is in a retracted configuration so that the rotor can be rotated. In some applications, the piston may be vertically oriented, such that gravitational force urges the piston into the unretracted configuration in the absence of a sufficient retaining force.
In one example, a tidal turbine yaw drive system (YDS) may employ a vertically oriented rotor lock having a mechanical piston assembly as described above. For these systems, a typical piston may weigh hundreds of pounds, thereby necessitating a large retention force, such as by an internal hydraulic pressure, to maintain the piston in a retracted configuration. However, in the event of loss of the hydraulic pressure due to failure, the piston is in danger of being urged into the unretracted configuration by gravity, thereby preventing the YDS from being unlocked and allowed to rotate.